1. Field of the Invention
The present invention relates to a walking assisting device for assisting a user in walking.
2. Description of the Related Art
Conventionally, as with this type of walking assisting device, there is known a trunk attachment portion attached to the user's trunk, a thigh attachment portion attached to a thigh of a user's leg with being connected to the trunk attachment portion via a hip joint portion corresponding to a human hip joint, a crus attachment portion attached to the crus of the user's leg with being connected to the thigh attachment portion via a knee joint portion corresponding to a human knee joint, and a foot attachment portion attached to a user's foot with being connected to the crus attachment portion via an ankle joint portion corresponding to a human ankle joint. Driving sources which drive the joint portions are provided coaxially with the joint portions, respectively (refer to Japanese Patent Laid-Open No. 2003-220102, for example). This type of walking assisting device is capable of assisting the user in walking by applying an assist moment from a driving source for the hip joint portion to the user's thigh via the thigh attachment portion, applying an assist moment from a driving source for the knee joint portion to the users crus via the crus attachment portion, and applying an assist moment from a driving source for the ankle joint portion to the user's foot via the foot attachment portion.
The above conventional walking assisting device is capable of assisting all movements of the user's thigh, crus, and foot, the thigh and the crus are restrained by the thigh attachment portion and the crus attachment portion. However, the user has an extremely constrained feeling. In addition, it is necessary to provide the driving sources for the joint portions such as the hip joint portion, the knee joint portion, and the ankle joint portion, which increases the cost disadvantageously.
In order to solve the above problem, it is conceivable to adapt the walking assisting device to include a load transfer portion, a foot attachment portion attached to the user's foot, and a leg link between the load transfer portion and the foot attachment portion wherein a force generated by the leg link is transmitted to the user's trunk via the load transfer portion. According thereto, the walking assisting device can assist walking by reducing the load on the user's leg by means of the force from the leg link transmitted to the user's trunk via the load transfer portion. Furthermore, it is possible to reduce the constrained feeling by making the leg link freed from the user's leg. In this condition, if the leg link includes an upper first link which is connected to the load transfer portion via a first joint portion, a lower second link which is connected to the foot attachment portion via a second joint portion, a middle third joint portion which connects the first link to the second link in such a way that they can bend and stretch freely, and a driving source which drives the third joint portion, the load on the user's leg can be reduced. This is accomplished by generating a force in the direction of decreasing a flexion angle of the third joint portion (in the direction of extending the leg link) by means of the driving source.
In the above, the leg link is freed from the user's leg and a force of bending the knee joint is not applied to the user's leg even if the leg link is bent in a condition where the user stands upright with his leg extending straight. This, however, causes the third joint portion of the leg link to project forward of the user's knee joint when the user stands upright and it brings discomfort to the user. Therefore, it is desirable that the flexion angle of the third joint portion is zero degree. In other words, the leg link is extended with the user's leg extending straight. This, however, causes a problem described below.
Specifically, in the case of the leg link which bends and stretches at the third joint portion, the extension speed of the leg link becomes zero when the flexion angle of the third joint portion reaches zero degree, where the extension speed is obtained by differentiating the length of the leg link (the length of a line segment between the first joint portion at the upper end of the leg link and the second joint portion at the lower end of the leg link) with respect to the flexion angle of the third joint portion. The result is a loss of controllability in the direction of extending the leg link, in other words, in the direction of pushing up the load transfer portion. Therefore, if the walking assisting device is adapted to have a zero degree of flexion angle of the third joint portion with the user's leg extending straight, it cannot appropriately control the upward force of the load transfer portion generated by the leg link so as to cope with a change in load even in a situation where the load changes because the user stands on one leg with the leg extending straight or the like. It is therefore necessary to prevent the loss of the controllability in the direction of pushing up the load transfer portion by bringing the leg link to be bent more or less with the user's leg extending straight, which results in bringing discomfort to the user.
In view of the above problem, an object of the present invention is to provide a walking assisting device that can be used by a user without feeling uncomfortable by enabling a leg link to be extended with a user's leg extending straight while maintaining the controllability in the direction of pushing up the load transfer portion also when the leg link is extended.